In recent years, a high dielectric constant insulating film (high-K insulating film) has been used as a gate insulating film and a capacitor insulating film in a semiconductor device. As such a high dielectric constant insulating film, for example, an insulating film made of metal oxide having a high dielectric constant, such as HfO2, is known.
In a semiconductor device, in order to secure a channel length in a transistor, increase the capacitance of a capacitor or the like, a trench is formed in a surface of a semiconductor substrate and metal oxide films (a gate insulating film and a capacitor insulating film) are formed on the surface in which the trench is formed. To this end, it becomes important to form a conformal metal oxide film with good step coverage.
In this connection, as a method of forming a metal oxide film, a chemical vapor deposition (CVD) method, an atomic layer deposition (ALD) method and the like are known. Among these, the ALD method has attracted attention since it can obtain a conformal metal oxide film. The term “conformal” used herein means that followability to the shape of a surface to be processed (surface on which a metal oxide film is formed) of a workpiece to be processed by the ALD method is excellent and the metal oxide film has an even thickness distribution.
As one example of a method of forming a metal oxide film using the ALD method, there has been used a method of forming a film made of HfO2 by forming a precursor layer on a substrate using tetrakis(dimethylamino)hafnium (TDMAH) as a precursor, followed by oxidizing the precursor layer with H2O.
However, the conventional method fails to obtain a conformal metal oxide film when a process (ALD process) of forming a metal oxide film is performed under low temperature conditions.